Manufactured fire-logs, fire starters and pellets for fireplaces and stoves are well known and widely used as a convenient heat source, as well as for the aesthetic enjoyment of a natural fire. The higher burn rate, longer burn time, and higher energy density make processed fire-logs an attractive alternative to natural wood. Furthermore, wood has many valuable uses and is accordingly in increasingly shorter supply. The desire to reduce wood consumption to a sustainable rate and to reduce the significant deforestation currently occurring worldwide, adds additional motivation to finding an alternative fuel source. In addition, decreasing landfill capacities have generated motivational incentives for finding alternative uses for waste by-products currently being dumped in landfill sites.
In a study by David A. Tillman, The Combustion of Solid Fuels and Wastes published in 1991, the combustion of solid fuels and wastes (including coffee waste) is suggested as potentially economical in raising process energy, generating electricity, and reducing the volume of municipal waste in landfills. The combustion of solid fuel particles--such as biomass, fossil fuels and municipal refuse--in an industrial furnace, boiler or kiln at high rates is investigated. The many advantages of coffee as a fuel source are not apparent from this study. Furthermore, no proposal is made for the production of processed solid fuels or domestically combustible fuels.
Prior art manufactured logs for domestic use have not been entirely satisfactory either in burn characteristics or in costs. The main advantages of processed fire-logs generally include long burn time, easy lighting characteristics, and convenience of use for preparation or maintenance of the fire. As a replacement for natural wood fires, processed logs offer the convenience of not having to stoke the fire to ensure a consistent flame. One log typically burns for 2 to 4 hours, depending on the size of log. However, these advantages are not unqualified. In order to achieve both a substantial flame and a quick ignition time, a significant amount of wax is used. The high combustion rate in combination with a limited air supply available in most modern houses typically results in incomplete combustion, which in turn leads to a buildup of soot and creosote in the flue. Repeated use of such prior art fire-logs can create a fire hazard. In fact, due to the seriousness of this problem, insurance companies recommend that consumers alternate between the use of processed fire-logs and natural wood fires, in addition to frequent cleaning of combustion apparatus.
Not only does the excessive use of wax represent a safety hazard due to the build-up of soot, it also means that the consumer is provided with an aesthetically less pleasing product than natural wood fires. While the substantial use of wax promotes faster ignition, the flame height for the later stages of combustion is significantly lower than when a fire-log is first lit. Consequently, it is difficult for a user to enjoy a flame comparable to a well-maintained natural wood fire.
A further disadvantage of fire-logs high in wax is the pollution produced during combustion. The volatility of wax causes a fast, sooty initial burn that ejects copious amounts of combustion by-products including soot and carbon monoxide into the atmosphere. In addition, some prior art manufactured fire-log compositions contain substances which are toxic or potentially toxic when combusted. There therefore exists a need for a safe, clean burning fire-log that maintains good flame consistency over and extended period of time.
A processed fire-log is disclosed in U.S. Pat. No. 5,393,310 issued to Wollen in 1995, which incorporates a large proportion of waste products, namely grass clippings and leaves. Wollen's primary goal is to use the composition to reduce yard waste in the waste stream while providing a burnable fuel. Leaves and grass clippings alone, however, do not provide a high energy fuel source, and even with the addition of significant amounts of paraffin wax such logs have a low calorific value. Wollen also suggests that the grass clippings be incorporated directly from the lawn without further processing, which introduces a higher moisture content that may interfere with combustion.
In response to pressures on the supply of petroleum waxes, and hence their increasing cost, U.S. Pat. No. 4,326,854 which issued in 1982 to Tanner, discloses a fire-log made of a liquid combustible by-product fuel component combined with a cellulosic or ligno-cellulosic particulate that serves as a carrier for the fuel component. The carrier provides a combustible skeleton of solid material such as sawdust or other cellulosic particulate incorporated at between 25% and 70% by weight, and preferably about 35%-40% by weight, with a binder fuel component comprising a liquid combustible by-product that is solidified by either polymerization or neutralization by the addition of various chemicals. The preferred liquid by-product fuel component is molasses. As one of many examples, Tanner tested a composition containing 60 parts (by weight) liquid vegetable pitch fuel component, 6 parts oleic acid, 3 parts caustic soda, and 37 parts coffee grounds as a carrier for the fuel component. Any advantage from using spent dried coffee grounds as a fuel source, such as cleaner burn and higher energy yield, were not recognized by Tanner.